Add test for safe-compare

src/auth/test/safe-compare.test.ts

+import safeCompare from '../safe-compare'
+
+const hmac = '7c66606415117ff9744a2a9b2be1712a15928b5ef474ab1a9ff5dc36b7dcaed8';
+
+describe('safeCompare', () => {
+  it('returns true when values are the same', () => {
+    expect(safeCompare(hmac, hmac)).toBe(true);
+  });
+
+  it('returns false when values are different', () => {
+    expect(safeCompare(hmac, 'not hmac')).toBe(false);
+  });
+});